Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2021
Publication Date: 3/4/2021
Citation: Chen, X., Sprott, J.A., Evans, C.K., Qin, R. 2021. Evaluation of Pacific Northwest winter wheat cultivars to fungicide application for control of stripe rust in 2020. Plant Disease Management Reports. 15:CF030.
Interpretive Summary: Stripe rust is one of the most destructive diseases of winter wheat in the Pacific Northwest, and the disease is controlled by planting resistant varieties and applying fungicides if varieties do not have adequate resistance. This study was conducted to determine yield losses by stripe rust and responses to fungicide application for 23 winter wheat varieties widely grown in the U.S. Pacific Northwest plus a susceptible check in a field near Pullman, WA during the 2019-2020 growth season. For the spray plots, fungicide Quilt Xcel was applied at the beginning of the rust season and again at the flowering stage. Stripe rust severity was recorded four times, and grain test weight and yield were measured for each plot at harvest. Relative area under disease progress curve (rAUDPC) was calculated using the severity data. The fungicide application significantly reduced stripe rust rAUDPC by 95.6% in the susceptible check and rust reduction was also signifcant in 11 of the 23 commercially grown varieties. The fungicide application significantly increased grain test weight of the susceptible check by 16.2 pounds per bushel and 13 of the 23 commercial varieties by 1.3 to 6.7 pounds per bushel. Significantly higher grain yield was observed in the susceptible check and 12 commercial varieties of the sprayed plots than the non-sprayed plots, whereas the 11 remaining varieties did not have significant diffences in yield, indicating adequate resistance. Based on the yield data, stripe rust caused yield loss of 62.4 bu/A (48.6%) for the susceptible check and 17.4 bushels per acre (11.6%) on average for the commercial varieties. The results are useful for managing stripe rust based on individual winter wheat varieties.
Technical Abstract: This study was conducted in a field near Pullman, WA to evaluate the control of stripe rust with fungicide applications on major winter wheat cultivars grown in the U.S. Pacific Northwest and assess yield loss caused by the disease. Winter wheat genotype 'PS 279' was used as a susceptible check, and 23 cultivars were selected based on their high acreage planted in the state of Washington in 2019. The 24 entries were arranged in a randomized split block design based on fungicide application, with four replications. They were seeded in rows spaced 14-in. apart at 60 lb/A (99% germination rate) with a drill planter on 31 Oct 19. The plots were 4.5-ft in width and 14.8 to 16.5-ft in length. Ammonium nitrogen fertilizer was applied at 100 lb/A at the time of planting and again on 22 Apr 20 at the same rate when plants were at late tillering stage (Feekes 3). Herbicides (Huskie 15.0 fl oz/A + Axial XL 16.4 fl oz/A + Starane Flex 13.5 fl oz/A + M-90 10.4 fl oz/A) were applied on 8 May when wheat plants were at the early jointing stage (Feekes 5-6). On 28 May when most plants were at the late jointing stage (Feekes 8) and stripe rust was just 1% severity in the susceptible check plots, Quilt Xcel 2.2SE was sprayed at the rate of 14.0 fl oz/A mixed with 0.25% v/v M-90 in 16-gallon water/A and sprayed again at the same rate on 11 Jun when plants were at the heading stage (Feekes 10.1) and stripe rust in the non-sprayed PS 279 plots reached 10-15% severity. A 601C backpack sprayer was used with a CO2-pressurized spray boom at 18 psi having three operating ¼ in. nozzles spaced 19-in. apart. Disease severity (percentage of stripe rust infected foliage per whole plot) was assessed from each plot on 27 May at the late jointing stage (Feekes 8-9), 10 Jun at the heading stage (Feekes 10.2), 24 Jun at the late flowering stage (Feekes 10.54), and 30 Jun at the milk stage (Feekes 11.1) or 1 day before and 13, 27, and 33 days after the first time of the fungicide application. Plots were harvested on 13 Aug when kernels had 13 to 15% kernel moisture and test weight of kernels was measured. Area under the disease progress curve (AUDPC) was calculated for each plot using the four sets of severity data. Relative AUDPC (rAUDPC) was calculated as percent of the non-treated susceptible check. rAUDPC, test weight, and yield data were subjected to analysis of variance, and the effect of fungicide application on rAUDPC, test weight, and yield was determined in comparison with non-sprayed plots for each cultivar by Fisher’s protected LSD test. A natural infection of the stripe rust pathogen was first observed on PS 279 plants in the nursery on 5 May 20. Stripe rust reached 100% severity by 24 Jun at the late flowering stage (Feekes 10.54) in the non-sprayed susceptible check plots. The two applications of Quilt Xcel at 14 fl oz/A reduced rAUDPC by 95.6% in the susceptible check (PS 279) plots. The fungicide applications also significantly reduced rAUDPC of eleven commercial cultivars (UI Magic, Eltan, LCS Jet, Mela CL+, WB 528, Otto, ARS-Crescent, Curiosity CL+, Puma, SY Clearstone 2CL, and Kelding), and the reduction ranged from 8.5 to 78.8%. The fungicide applications significantly protected grain test weight of the susceptible check (PS 279) by 16.2 lb/bu and thirteen commercial cultivars (UI Magic, Eltan, LCS Jet, ORCF-102, Mela CL+, WB 528, Jasper, Curiosity CL+, LCS Artdeco, Puma, SY Clearstone 2CL, Keldin, and SY Ovation) by 1.3 to 6.7 lb/bu. The fungicide applications made significant yield differences for the susceptible check (62.4 bu/A more in the sprayed plots) and twelve commercial cultivars (UI Magic, Eltan, LCS Jet, ORCF-102, Mela CL+, WB 528, Jasper, Otto, ARS-Crescent, Curiosity CL+, Northwest Duet, and Bruehl) with 14.2 to 52.4 bu/A more grain in the sprayed plots. The remaining eleven commercial cultivars (Northwest Tandem, WB1529, LCS Ar